Crawling The Deep Web
A vast amount of Web pages lie in the deep or invisible Web. These pages are typically only accessible by submitting queries to a database, and regular crawlers are unable to find these pages if there are no links that point to them. Google's Sitemaps protocol and mod oai are intended to allow discovery of these deep-Web resources.
Deep Web crawling also multiplies the number of Web links to be crawled. Some crawlers only take some of the -shaped URLs. In some cases, such as the Googlebot, Web crawling is done on all text contained inside the hypertext content, tags, or text.
Strategic approaches may be taken to target deep-Web content. With a technique called screen scraping, specialized software may be customized to automatically and repeatedly query a given Web form with the intention of aggregating the resulting data. Such software can be used to span multiple Web forms across multiple Websites. Data extracted from the results of one Web form submission can be taken and applied as input to another Web form thus establishing continuity across the Deep Web in a way not possible with traditional web crawlers.
Read more about this topic: Web Crawler
Famous quotes containing the words crawling, deep and/or web:
“In the cold of Europe, under prudish northern fogs, except when slaughter is afoot, you only glimpse the crawling cruelty of your fellow men. But their rottenness rises to the surface as soon as they are tickled by the hideous fevers of the tropics.”
—Louis-Ferdinand Céline (1894–1961)
“The older woman’s love is not love of herself, nor of herself mirrored in a lover’s eyes, nor is it corrupted by need. It is a feeling of tenderness so still and deep and warm that it gilds every grassblade and blesses every fly. It includes the ones who have a claim on it, and a great deal else besides. I wouldn’t have missed it for the world.”
—Germaine Greer (b. 1939)
“Any newspaper, from the first line to the last, is nothing but a web of horrors.... I cannot understand how an innocent hand can touch a newspaper without convulsing in disgust.”
—Charles Baudelaire (1821–1867)